Add extern 'C' guards to eliminate -Wold-style-cast warnings in C++. (#10)
Add extern 'C' guards to eliminate -Wold-style-cast warnings in C++. (#10)

* Add extern 'C' guards to eliminate -Wold-style-cast warnings in C++.

* Comply with C90 by removing C++-style comment.

KOConchobhair/libpopcnt,kimwalisch/libpopcnt,KOConchobhair/libpopcnt,kimwalisch/libpopcnt